1. Field of the Invention
This invention relates to an electrophotographic photosensitive member comprising an organic photoconductor, more particularly to a lamination type electrophotographic photosensitive membcr provided by coating with a photosensitive layer with a laminated structure having a charge generating layer and a charge transporting layer.
2. Description of the Prior Art
The surface of the photosensitive layer of an electrophotographic photosensitive member is subjected directly to electrical, thermal and further mechanical external force in various processes in an electrophotographic copying machine, such as corona charging, toner developing, transfer onto paper, cleaning treatment, etc., and therefore the photosensitive layer is required to have durability against lowering in sensitivity or lowering in potential attributable to deterioration by ozone generated during corona charging, increase in residual potential or generation of friction or damage on the surface by scraping. Particularly, in a lamination type electrophotographic photosensitive member having a charge transporting layer provided by coating on a charge generating layer, the charge transporting layer is deteriorated by ozone generated during corona charging. For this reason, when image formation is carried out in repeated cycles, lowering in sensitivity will gradually be brought about. Alternatively, if a resin with high hardness is employed for the charge transporting layer for enhancement of resistance against external mechanical force, the coating characteristic may be unsatisfactory, or no sufficient sensitivity can be obtained. Thus, a very difficult problem is involved in choice of a resin from among a large number of resins in consideration of both electrophotographic characteristic and coating characteristic.
As the binder resin used heretofore in the charge transporting layer, polycarbonate, polymethyl methacrylate, polyallylate, polystyrene and polyester have been proposed. However, electrophotographic photosensitive members by use of these resins have many points to be improved such as insufficient mechanical strength, or the problem in manufacturing step caused by poor coating characteristic.